Measurements of directed, elliptic, and triangular flow in Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

TL;DR

This study measures anisotropic flow coefficients in Cu+Au collisions at 200 GeV, revealing mass ordering consistent with hydrodynamics and scaling behaviors across different collision systems.

Contribution

It provides detailed flow measurements in Cu+Au collisions and compares them with models and other systems, highlighting universal scaling properties.

Findings

Mass ordering observed for all three flow harmonics.

Flow coefficients scale with $1/( ext{eccentricity}_n N_{ ext{part}}^{1/3})$.

Results agree with hydrodynamic and transport model predictions.

Abstract

Measurements of anisotropic flow Fourier coefficients ($v_n$) for inclusive charged particles and identified hadrons $\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ produced at midrapidity in Cu+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV are presented. The data were collected in 2012 by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). The particle azimuthal distributions with respect to different order symmetry planes $\Psi_n$, for $n$~=~1, 2, and 3 are studied as a function of transverse momentum $p_T$ over a broad range of collisions centralities. Mass ordering, as expected from hydrodynamic flow, is observed for all three harmonics. The charged-particle results are compared to hydrodynamical and transport model calculations. We also compare these Cu$+$Au results with those in Cu$+$Cu and Au$+$Au collisions at the same $\sqrt{s_{_{NN}}}$, and find that the $v_2$ and $v_3$, as a function of transverse momentum, follow a common scaling with $1/(\varepsilon_n N_{\rm part}^{1/3})$.